This invention relates to diversity radio receivers.
In one class of diversity radio receivers, a plurality of antennas are positioned to receive signals transmitted from a single transmitter. The circuitry connecting the antennas to the rest of the diversity receiver reduces fading caused by multipath cancellation of the signals from the single transmitter. In some such receivers a signal indicating the strength of the received signal controls the circuitry in such a manner as to minimize multipath cancellation of signal.
In some prior art diversity receivers of this class the signal from the squelch circuit controls the switching of the receiver from antenna to antenna to obtain the best signal. A phase shift is imposed between the signal received from one antenna and the signal from the other antenna. In other prior art diversity receivers, signals from both antennas are added together and the phase is continually changed in accordance with changes in the sum of the signals. In still another type of diversity receiver of this class, the signals from the antennas are modulated with an average frequency carrier to remove phase shift components and the signals are added together to provide a total signal stronger than the individual signals received by each antenna.
The prior art space diversity receivers have the disadvantage of being relatively complex and thus expensive. Some are complex because the signals are applied from each antenna to a corresponding one of several portions of receivers before being added for final processing. Moreover, some of the circuits for correcting for phase shift, or for switching from antenna to antenna or receiver to receiver or for modulation of signals are complicated and expensive.